1. Field of Invention
The invention relates in general, to firearms, and more particularly to fixtures which mitigate the transfer of torque from the barrel nut to the firearms receiver during installation of the barrel.
2. Description of the Related Art
Firearms in the M16 family, which include but are not limited to, the AR10, SR25, AR15, and piston driven systems and other similar designs, have been in use with military, police, and civilian shooters for nearly 50 years. The M16 family of firearms includes a lower receiver having a stock coupled to the rear end which is connected to an upper receiver having a barrel coupled to the front end. The chamber end of the barrel is received by a portion of the upper receiver and threadedly secured in place. The threads of the upper receiver which receive the barrel nut are not timed in any way but require a minimum torque of 30 foot pounds to secure the barrel in place. The outer surface of the barrel nut has a series of spokes, with gaps formed between, which are used to apply torque to the barrel nut. In order to properly install the gas operating system of the firearm, a gap in the spokes must be in alignment with an opening in the front of the upper receiver. This alignment is required because the gap between the spokes facilitates the entry of either a piston or a gas tube, of the gas operating system, into the interior of the upper receiver. To achieve this required alignment, the barrel nut is often either under- or over-torqued. Both of these conditions present a variety of potential problems which include, but are not limited to, damage to the firearm, poor accuracy during normal operation or compromised operational reliability.
Indirect gas operated M16 type rifles, often referred to as piston driven, such as the design described in U.S. Pat. No. 7,461,581 (“the '581 patent”), are becoming increasingly popular within both the commercial and military markets due to the increased operational reliability offered by such systems. The vast majority of these new piston driven designs rely on the prior art barrel nut common to the M16 family of firearms and as such have inherited the flaws of this design. In addition to the trouble which can result from improper torque being applied to the barrel nut, these piston designs depend on a moving piston, which is supported by the spokes of the barrel nut, to operate. However, the spokes of the barrel nut were not designed for this purpose and, as a result, present a weak point in the operational reliability of these new piston driven designs. Over time some systems which rely on the prior art barrel nut fail because the spokes which support the piston directly, or a removable bushing which houses the piston, start to bend or break, rendering the firearm inoperable. Therefore a need exists for a barrel nut design that will remedy the foregoing and other deficiencies inherent in the prior art.
Installation of the legacy AR15/M16 barrel nut, even when done properly, results in the transfer of torque from the barrel nut to the firearms receiver during installation of the barrel. This is of particular concern when the receiver alone is being restrained by a fixture that is secured in place by vice. Torque is transferred to the receiver when so restrained because the annular flange of the barrel is resting against the forward face of the receivers threaded extension while the barrel nut is threadedly secured in place, More specifically, when the barrel is being secured in place, the barrel nut is rotated thereby depressing the annular flange of the barrel against the forward face of the receivers threaded extension. While the barrel nut is being rotated, the rotation force (torque) is transferred to the annular flange of the barrel. The rotation of the barrel, vicarious of the annular flange, is arrested by the receivers threaded extension. By preventing the rotation of the barrel, the receiver is absorbing a portion of the torque being applied to the barrel nut. This can result in the warping or cracking of the receiver and its threaded extension.
Damage resulting from this transfer of torque to the receiver may be mitigated or even eliminated when a proper predetermined torque value is applied to the barrel nut during the installation of the barrel. But, as discussed above, over torquing the barrel nut is often required in order to facilitate the proper alignment of a gap between the flanges of the prior art barrel nut with the gas tube opening on the face of the upper receiver. While the prior art barrel nut may be installed within the given range of 30 ft-lb to 80 ft-lb of torque, it is a common belief that torque applied at and near the upper end of this range is detrimental to the accuracy of the firearm in many cases. This degradation of accuracy is attributed to the receiver warping as a result of the barrel nuts installation. In order to minimize this transfer of torque from the barrel nut to the receiver, some gun smiths use vise blocks of differing designs to secure the barrels itself within a vice thereby preventing the receiver from resisting the rotation of the barrel during the installation of the barrel nut.
Prior art vise blocks have several deficiencies which become apparent during use. It is very difficult to secure a barrel within vice blocks with sufficient force so as to prevent its unintentional rotation during assembly, while at the same time not damaging the external finish of the firearm. It is also very difficult to predict how much force the user needs to apply to the vice in order to properly secure the barrel and thus prevent rotation without a period of trial and error. During this period of trial and error, the barrel will slip and rotate within the fixture when torque is applied to the barrel nut. Further, the use of vice blocks that secure about the barrel also requires that the gas tube or gas piston need to be removed in order to install a muzzle device. The removal of the gas system may be incidental and of little concern for work on a single rifle, but becomes very inefficient when work is being performed on an industrial scale. Thus a need exists for a fixture which aids in the installation of a barrel onto a receiver, that will remedy the foregoing and other deficiencies inherent in the prior art.